The present invention relates generally to seals between circumferentially registering slashfaces of nozzle segments in a steam turbine and particularly relates to spline seals between the slashfaces of the nozzle segments.
In steam turbines, there are static nozzles including stator vanes, i.e., airfoils, circumferentially spaced one from the other about a rotor mounting circumferentially spaced buckets. Each set of nozzles and buckets forms a turbine stage. The nozzles turn the steam flow into the buckets which, in turn, extract work from the steam flow. In steam turbines, it is critical to minimize or eliminate as many leakage paths as possible within the steam flowpath of the turbine and any secondary leakage circuits. While impulse steam turbines typically have a wheel and diaphragm construction, reaction steam turbines typically utilize a drum rotor construction. In an impulse design, the stage pressure drop is primarily taken across the stationary nozzle partitions whereas in the reaction design, the pressure drop is about equally divided between the stationary and rotating blades.
In the reaction style drum rotor construction, the nozzles mounting the partitions or stator vanes are slidably received in circumferentially extending dovetail grooves as individual nozzle segments. That is, the nozzle segments stack up one against the other in a circumferential direction. The nozzle segment has slashfaces at opposite ends, i.e., endfaces, that are typically angled with respect to the rotor axis to accommodate the sweeping airfoil turning shape of the nozzle. The slashfaces are extant on all stages of the high pressure and intermediate pressure steam turbine sections. Gaps are therefore extant between the slashfaces, the gaps essentially appearing as a result of machining tolerances of the segments and casing hooks, assembly methods and operational pressures and temperatures. These slashface gaps can be sufficiently large to produce substantial leakage between the differential pressure regions forward and aft of the nozzles. The problem is compounded due to the larger number of nozzle segments on a typical reaction turbine design as compared with an impulse turbine design. Thus, the gaps between the slashfaces between adjacent nozzle segments add up to a significant leakage area which, if not accounted for, causes increased efficiency losses. Accordingly, there is a need to minimize or eliminate the steam leakage flowpaths between the slashfaces of adjacent nozzle segments in a steam turbine.